SmogRank / World / Canada / Ontario / September 2026

Most polluted cities in Ontario, Canada, September 2026

29 cities in Ontario, Canada ranked by their average PM2.5 over the 30 days. Worst: Hamilton at 5.8 µg/m³, #1,843 of 2,949 cities in the world. Cleanest: Peterborough at 3.6. A city needs measurements on 70% of the days to be ranked.

Ranked by unhealthy days: the share of each city's measured days with a daily mean over 35.4 µg/m³ (US AQI 101+), Unhealthy for Sensitive Groups or worse on the US EPA's scale. Ties go to the higher average.

← Hamilton 0% 0.75%0

Every city in Ontario, Canada ranked for September 2026, one column each, ranked by unhealthy days: height is the share of its measured days that were unhealthy, colour its average. Point at it to read a city; tap to open it.

1Hamilton
0%
2Brantford
0%
3Barrie
0%
3Cornwall
0%
3Newmarket
0%
6Windsor
0%
7London
0%
7Nepeanlow-cost sensors
0%
7St. Thomas
0%
7Toronto
0%
11Guelph
0%
11Kitchener
0%
13Milton
0%
13Oakville
0%
13St. Catharines
0%
16Sarnia
0%
17Brampton
0%
17Waterdown
0%
19Greater Sudbury
0%
20Chatham
0%
21Belleville
0%
22Mississauga
0%
23Alliston
0%
23Kingston
0%
23Ottawa
0%
26North Bay
0%
27Parry Sound
0%
28Sault Ste. Marie
0%
29Peterborough
0%

Low-cost sensors: consumer units, counted only in cities with no government-grade monitor; they read close to reference monitors on the whole, but 15 to 25% high in humid air. How we use them.

Good0–50

Moderate51–100

Sensitive groups101–150

Unhealthy151–200

Very unhealthy201–300

Hazardous301+

The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales

All cities in the world, September 2026 · All cities in Canada, September 2026 · Ontario now

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SmogRank, most polluted cities in Ontario, Canada, PM2.5, September 2026, smogrank.com/ca/region/ontario/history/2026-09 (accessed 6 Oct 2026).

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You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.